Spring Has Sprung, Sort Of

The disconnect between calendar Spring and that recognized by animals continues. March 20 has come and gone but there is a great deal of northward migration still to come. On the other hand warm weather has brought out many insects, some frogs are calling, and our first trans Gulf warbler, the marvelous hooded, has arrived in our FL yard.

Nothing says spring more than beautiful butterflies flitting around the yard. While we have had zebras all winter, the appearance of this newly emerged and brilliant male Gulf fritillary definitely shows how the season is changing. The males of this species are much brighter than the females and presumably attract females by their showy coloration. This pattern seems to be an example of toxic Muellerian mimicry of the milkweed-feeding monarchs, although based on chemicals derived from passionvines.

Some other insects attracting attention this time of year are the dragonflies, that need warm sunny weather for their complex flight. A huge twilight darner flew into our open door and gave me an opportunity to examine it up close and personal. This species is limited to FL and extreme southern GA. In contrast ferocious eastern pondhawks are quite common now and will be seen widely throughout the eastern US. The males are bluish and the females greenish, another of many examples of sexual dimorphism in dragonflies. I watched a female laying eggs in the water and her mate flew immediately above her to protect her from intruding males. The complexity of the reproductive patterns in these primitive insects amazes me.

I always make a number of interesting observations of wildlife in our bay-front yard and the recent period in late March has been no exception. A great blue heron came up to one of our bird baths and managed to get some fresh water to drink despite the unsuitability of its bill for this purpose. There is of course no natural fresh water on our island so many birds are attracted to fresh water in a bath, but I was surprised that the great blue was interested since it presumably has a salt gland to allow it to drink salt water. A catbird also came to the bath and illustrated that it has yet to migrate north to its breeding grounds; they do not breed in southern FL strangely enough. Great egrets often forage in the yard searching mainly for brown anoles; indeed this exotic lizard is now the basis of the food chain for many native birds and snakes. But this egret had caught a SE five lined skink, a slippery and potentially toxic prize which is reputed to be poisonous to eat. On our dock a spotted sandpiper, just starting to get its lovely spotted breast, lingered for a while on its way north to breed.

At nearby estuarine Lemon Lake we have continued to enjoy the fabulous roseate spoonbills which are feeding on prey concentrated by declining water levels. They will be breeding nearby, in contrast with the few remaining blue-winged teal which should already have been winging their way northward.

So while spring is definitely underway, many species are still taking their sweet time to go north. Are they lazy, addicted to FL sunshine, or just inefficient? It seems likely that the timing of migration is often set to coincide with the most appropriate period in which to establish territories and obtain food for young on breeding grounds. Thus species and individuals which breed very far north may lag behind those which are moving to lower latitudes.

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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